This invention relates to current or power limiting circuits and, more particularly, to self-protecting limiting circuits for driving inductive loads, for instance, requiring predetermined average amounts of electrical power.
A variety of solid state, discrete current or power limiting circuits are known in the art for performing various functions. Such circuits generally must deliver at least a minimum amount of power to operate a load but not dissipate more than a maximum amount of power to protect the load or the circuit itself for both. Some of these circuits are complex and others demand the use of expensive discrete power transistors which are required to dissipate large amounts of power under at least some operating conditions. Such power transistors usually must be provided with bulky, expensive heat sinks which keep them within their safe areas of operation.
In many modern applications it is desired that inductive loads, for instance, be driven by monolithic integrated circuits because of cost and reliability considerations. Also, such circuits take up less space and do not weigh as much as corresponding discrete circuits. It is also desirable for such circuits to generate a minimum amount of heat. Since inductive loads often require several amperes of current, driver circuits therefor have traditionally required output power transistors. Unfortunately, it is difficult to build efficient power transistors in monolithic integrated circuit form and it is also difficult to effectively heat sink integrated circuit transistors. Thus, integrated circuits have not traditionally included the final stage load driving devices. A prior art circuit is shown in FIG. 1 and described hereinafter in more detail.